This circuit is being used for mains detection. Input is being fed directly from 220V 50Hz mains and output goes to Arduino which is running on 3.3V.
Theoretically the optocoupler LED should burn out during reverse polarity of 220VAC in the circuit given below:
Here is the voltage graph which appears across the LED of opto-coupler:
It shows a peak reverse voltage of 50V only instead of expected 220V (at least that's what I expected). However 50V alone should be able to destroy the LED.
I have used this circuit in a project and it has been working perfectly for about 6-7 months. Why does this circuit work?